Means and method for controlling surface resistance of insulators



Nov. 12, 1929. A. o. AUSTIN MEANS AND METHOD FOR CONTROLLING SURFACERESISTANCE OF INSULATORS Original Filed Oct. 20, 921

By 7. m

IN 125N701? A TTORA'EY Patented Nov. 12,1929

UNITED STATES PATENT OFFICE ARTHUR O. AUSTIN, OF BARBERTON, OHIO,ASSIGNOR, BY MESNE ASSIGNMENTS, TO

THE OHIOBRASS COMPANY, OF MANSFIELD, OHIO, A CORPORATION OF NEW JERSEYMEANS AND METHOD FOR CONTROLLING SURFACE RESISTANCE OF IN SULATORSApplication filed October 20, 1921, Serial No. 508,987. Renewed November15, 1926.

This invention relates to insulators designed especially for hightension work and has for its object the provision of controlling meansfor the surface resistance thereof, which shall improve the operationandv partly in section showing one embodiment of the invention. 7

The insulator member shown consists of attaching members 10 and 13cemented to a dielectric member 11. The flange 12 of the dielectricmember provides a path for surface leakage between the attachingmembers, and also, increases the distance thru the air between thesemembers, so that the high voltage may be carried without fiash-overbetween the holding members.

When a high voltage is applied between the attaching members there is atendency for charging current to flow out over the surfaces 14 and 16.These surfaces may be flooded with streamers which tend to reduce thedrop in voltage along the same, particularly if the charging current inthe streamer is large and combined with surface leakage current.

Owing to the relatively small diameter of the leakage path adjacent theattaching members the concentration of leakage current must necessarilybe greater near the attaching members. This is due to the fact that thewidth of the leakage path at any distance from the attaching members isdirectly proportional to the diameter of the insulatin member at thatdistance. From this it fo lows that the concentration of leakage andcharging current may be relatively large on the zone such as 14.adjacent the attaching member 13. When this leakage current flows out inthe form of streamers the potential drop is likely to vary considerablyas the current in the streamers may be varied greatly by slightdifferences. A streamer which tends to start first charges a largersurface and draws more current, thereby cutting down its resistance.This will give the streamer a greater shunting effect on the surface andtend to lower the etficiency or carrying capacity of the surface orinsulator.

If the surface 14 which is highly stresesd is roughened or covered witha porous material which may be made slightly conducting by impregnatingwith conducting material, the surface discharge may be eliminated and avarying surface resistance established, the surface resistance gradientor rate of change of surface resistance being regulated to suit theparticular conditions. This graded surface may be produced by using aproper sanding applied in accordance with my prior Patent N 0. 1,284,975or a porous layer, or body composition may be applied to the maindielectric member and burnt with the pieces. This porous layer may beeasily produced by decreasing the fluxing material in the regular bodycomposition, or by other means, or the material may be materiallydifferent from the main body composition, it simply being necessary toproduce a material which is porous electrically.

Another method of producing the surface is by applying a layer of cementsuch as Portland cement by an air blast, or other means. This may beheld to the am body member by means of a sanded su flace such asdisclosed in my previous patent referred to above.

There are several means of producing the graded resistance. One of themethodsis to impregnate or coat the surface with a material which willreduce its resistance. This should be preferably conducting materialwhich would tend to maintain a resistance under operating conditions,such as calcium chloride which would absorb water from the atmosphere.Another method of use is to simply provide the proper surface and allowthe electrical discharge in the same to form nitrates which will lowerits resistance automatically where the stress is great.

Where this method is used the porous surface has a decided advantage, inthat there is a strong tendency to break up any distinct streamer sothat the shunting effect becomes negligible. This is due to the factthat any streamers forming on the surface will tend to be drawn downinto the coating where the resistance will prevent spreading. In somecases the roughened surface is sufficient, in that, it will catch dirtwhich will lower the resistance of the same automatically.

Where the surface stress is high, there is a tendency to depositconducting material from the air. This accumulation, particularly wherea roughened surface for retaining same is provided will grade thesurface materially.

Where a varying effect is to be produced by grading, the same may beaccomplished by properly regulating the thickness of the coating asshown in 14, or by dividing the resistance grading surface into zones inseries as 14 and 15, which may be made in different ways, or as 16 and17 which may closely approximate each other.

Grading the surface is particularly effective where it is desired toincrease the electr o-static capacity so as to prevent over-stress inmembers which may be a part of a series of insulators as a membercarrying the high est stress in a pin type insulator, or the endsections in a suspension string.

Where the surface resistance is high and the charging current isappreciable the heat generated may be used to advantage in drying offthe insulator. This will tend to maintain the carrying capacity of aninsulator in fogs, or other severe conditions. This is particularlyapplicable to radio insulators such as deck bushings, and insulators onthe aerials which are used on board ships. Unless there is a dry zonethe leakage tends to prevent efficient radiation, so that a limitedamount of heating on the insulator which will roduce a dry zone may bepatricularly bene cial for it is evident that if the insulator is warm,and although the same may be covered by a spray, a zone would dry offvery quickly.

The invention is not limited to the form shown, but is applicable to allsurfaces where it is desired to control the electrical gradient due tocharging or leakage current.

The method is beneficial in preventing a concentration of stress where asmall-electrode is in contact with a large surface which might otherwisecause a high concentration of stress at points of contact betweenelectrode and dielectric.

I claim 1. An insulator having a dielectric mem ber the surface of whichpresents a path of varying extent for leakage and charging currents anda coating on the surface path of said dielectric member of a nature toreduce the resistance thereof, said coating being arranged to produce agraded variation in the resistance per unit surface the resistance perunit surface increasing from the more restricted to the less restrictedportions of said ath. p 2. An insulator comprising a dielectric memberthe surface of which provides a path for leakage and charging currentswhich varies in width, and a pervious coating for said surface path of anature to reduce the surface resistance thereof, said coating beinggraded to decrease in thickness from the narrower to the wider portionsof said path.

3. An insulator .comprising a dielectric member having an attachingmember secured thereto, and means immediately adjacent said attachingmember and having graded conductivity per unit area decreasing away fromsaid attaching member on the surface of said dielectric member adjacentsaid attaching member for reducing the surface resistance of saiddielectric member, while said surface farther removed from saidattaching member is substantially free from said resistance reducingmeans.

4. An insulator comprising a dielectric member having an attachingmember secured thereto, and means immediately adjacent said attachingmember on the surface of said dielectric member for producing a gradedvariation of the surface resistance thereof adjacent said attachingmember so that said surface resistance per unit area increases outwardlyfrom said attaching member.

5. An insulator comprisin a dielectric member having attaching mem erssecured to opposite sides thereof, the surface of said dielectric memberbeing arranged to radiate outwardly from said attaching members andhaving pervious coatings on the portions of said surface adjacent saidattaching members of a nature to retain'material for reducing thesurface resistance of said dielectric member on the restricted'portionsof the path of charging and leakage currents between said attachingmembers, while the portions of said surface farther removed from saidattaching members are made smooth to shed foreign matter.

6. An insulator comprising a dielectric member having attaching memberssecured to opposite sides thereof, the surface of said dielectric memberbeing arranged to radiate outwardly from said attaching members, saidsurface adjacent said attaching members being coated with materialhaving openings therein for retaining matter of a nature to decrease thesurface resistance of said dielectric member said coating being gradedto decrease in thickness in an outward direction from said attachingmembers.

7. The method of grading the surface resistance of a dielectric membercomprising the steps of providing a retention coating for a portion ofsaid surface where relatively low resistance is desired while otherportions therof are smoothly coated to avoid deposits thereon andsubjecting said surface to the action of electric currents passingthereover to cause a deposit of resistance reducing ma terial on theportions of said surface where the current is most concentrated.

8. The method of grading the surface resistance of an insulator havin adielectric member and attaching mem ers secured thereto comprising thesteps of providing a retention coating on the surface of said dielectricmember adjacent said attaching members while portions of said surfaceremoved from.

said attaching members are free from such coating and subjecting saidattaching members to high potential differences to cause charging andleakage currents to flow over the surface. of said dielectric member,thusdepositing resistance reducing material on said retention coating atplaces where said currents tend to concentrate.

9. The method of controlling the surface resistance gradient of aninsulator having a dielectric member and attaching members securedthereto comprising the steps of providing a retention coating on thesurface of said dielectric member adjacent said attaching members, saidcoating being varied in its ability to retain conducting material andhaving greater retentive ability where greater conductivity is desiredand permitting the accumulation of resistance reducing material on saidretention coating;

10. The method of controlling the surface resistance gradient ofaninsulator having a dielectric member and attaching members securedthereto comprising the steps of coating the surface of said dielectricmember adjacent said attaching members with pervious material saidcoating decreasing in thickness outwardly from said attaching membersand permitting the accumulation of resistance decreasing matter on saidpervious coating.

In testimony whereof I have signed my name to this specification on this13th day of October, A. D. 1921.

ARTHUR O. AUSTIN.

